This is a platform bug. See this topic for more details. OutSystems should be aware of it (I informed them a while ago), but it doesn't hurt to let them know you encountered it as well (support@outsystems.com).

Changing to LongIntegerToIdentifier did work. But I don't have to choose for the platform if the value 1 should be intepreted as a IntegerToIdentifier or all LongIntegerToIdentifier. The value is in range of both types and the result should be and Indentifier and it should matter if it's coming from an Integer or LongInteger.